Coated carbon brake disc materials

Abstract

Antioxidant coating compositions containing 10-75 wt % H 2 O, 20-65 wt % H 3 PO 4 , 0.1-20 wt % alkali metal mono-, di-, or tri-basic phosphate, 0-2 wt % hydrated boron oxide, 0-18 wt % KH 2 PO 4 , 3-10 wt % of a transition metal oxide, and 0-20 wt % hydrated manganese phosphate, 0-25 wt % Al(H 2 PO 4 ) 3 , and 0-10 wt % Zn 3 (PO 4 ) 2 , provided that at least one of Al(H 2 PO 4 ) 3 , Zn 3 (PO 4 ) 2 , and hydrated manganese phosphate is present. Also, brake discs made from carbon composite articles having their surface treated with certain antioxidant coatings. During a manufacturing process, carbon matrix 15 of brake disc 11 is covered on its outer and inner edges with antioxidant layers 19 and portions of the working surface of brake disc 11 may also be covered with antioxidant layers 13 , potentially decreasing the fitness of the brake disc for service. In accordance with this invention, brake disc 12 is manufactured from brake disc 11 by the removal from its working surface of antioxidant layers 13.

1. A brake disc comprising a carbon composite article, the surface of which article has been treated with an antioxidant coating which contains from about 3 through about 10 weight-% of a transition metal oxide, said transition metal oxide being selected so that the antioxidant coating:
 a) protects the carbon composite against oxidative weight loss,  
 b) does not abrogate friction properties of the composite, and  
 c) remains visible after charring at 1600° F. for 6 hours.  
 
     
     
       2. A brake disc comprising a carbon composite article, the surface of which article has been treated with an antioxidant coating which comprises from 10-75 wt % H 2 O, 20-65 wt % H 3 PO 4 , 0.1-20 wt % alkali metal mono-, di-, or tri-basic phosphate, 0-2 wt % hydrated boron oxide, 0-18 wt % KH 2 PO 4 , 3-10 wt % of a transition metal oxide, and 0-20 wt % hydrated manganese phosphate, 0-25 wt % Al(H 2 PO 4 ) 3 , and 0-10 wt % Zn 3 (PO 4 ) 2 , provided that at least one of Al(H 2 PO 4 ) 3 , Zn 3 (PO 4 ) 2 , and hydrated manganese phosphate is present, said transition metal oxide being selected so that the antioxidant coating:
 a) protects the carbon composite against oxidative weight loss,  
 b) does not abrogate friction properties of the composite, and  
 c) remains visible after charring.  
 
     
     
       3. The brake disc of  claim 2 , wherein the transition metal oxide comprises CoCr 2 O 4 . 
     
     
       4. A method for protecting a carbon composite friction article against oxidative weight loss, which method comprises treating the surface of the composite article with an antioxidant coating which contains from about 3 through about 10 weight-% of a transition metal oxide, wherein the antioxidant coating does not abrogate friction properties of the composite and wherein the antioxidant coating remains visible after charring at 1600° F. for 6 hours. 
     
     
       5. The method of  claim 4 , which method comprises a preliminary step of configuring the carbon composite friction article as a brake disc. 
     
     
       6. The method of  claim 5 , which method comprises a subsequent step of removing said antioxidant coating from a working surface of the brake disc.